I’d heard of cavitation before, probably in Hunt for Red October, but never would have imagined that noisy submarine propellers could be connected to concrete dam spillways.
When a "sustained" Sonoluminescence effect/method was discovered, physicists were racing to explain the phenomenon. The effect was so radical that physicists were calling other physicists "crazy" on each others' proposed theories.
There is much that will be discovered in this "classified realm" in energy. That is the field I am working in now.